1. Field of the Invention
The invention relates to the use of oxyethylated diphenylamines as sun screen agents in cosmetic preparations.
2. Description of the Prior Art
It is known that the range of sunlight or artificial light sources between 280 and 320 nm referred to as ultraviolet-B-radiation is responsible for the formation for erythema of the human skin. The maximum effectiveness of the ultraviolet radiation for the formation of erythema lies at 297 nm if the radiation intensity is equal for all wave lengths. In the case of sunlight with radiation of varying intensity, this maximum shifts to 308 nm. By using suitable filter substances for the ultraviolet-B range, it is possible to prevent or at least delay the formation of erythema. The pigment formation of the skin that is tanning should, however, be retained.
In addition, ultraviolet radiation is an important influencing factor in the aging of polymers and may, for instance, cause degradation of certain dyestuffs so that filter substances are almost essential as stabilizers for such products.
During the past forty years, a great number of chemical compounds has been examined for their filtering effects in the ultraviolet-B range. Whether or not a substance absorbs light in the ultraviolet range and is also a usable sun screen for the human skin is determined by several factors. In addition to the high filtering effectiveness in the erythemal range, the substance should have a relatively high permeability in the ultraviolet-A range. It should also be as compatible with the skin and the mucous membrane and must not be toxic. Finally the substance should not be sensitive to oxidation and should not be altered or discolored by ultraviolet radiation. A preparation containing the substance should be storage stable, should not have an intrinsic odor, and should be compatible with commonly used cosmetic ingredients.
The known ultraviolet screening substances frequently have the drawbacks that they are unstable to ultraviolet radiation or visible radiation and/or air during storage, that they are transformed into colored decomposition products, that they soil clothing, or that they can even damage the skin. In practice, relatively few substances, which more or less meet the listed requirements have become accepted as is indicated, for instance, in Chemische Rundschau 24, (1971) page 1097.
It is known from German Pat. No. 1,543,387, that polyalkoxylated para-aminobenzoates can be used as sun screen agents. The polyalkoxylation is carried out by reacting the corresponding carboxylic acids or carboxylates with alkylene oxides in the presence of an alkaline catalyst. The alkylene oxides may be added to the carboxylic acid or to the amino group.